Sediment density flow deposits at the channel-lobe transition zone: an example from late Tortonian of the Sorbas Basin, SE Spain

The subaqueous sediment density flows (SDF) in Mizala (Sorbas Basin, SE Spain) were deposited during the late Tortonian in a middle submarine fan system, near the channel-lobe transition zone. Channel and lobe deposits comprise 6 facies types interpreted as debrites, high-density turbidites, low-density turbidites and hemipelagic autochtonous deposits. The results of this study show the flow transformation of the SDF at the channel-mouth as a consequence of hydraulic jumps. A relative sea-level rise might have conditioned the stacking pattern of the channel-lobe system. This study contributes to understand the sedimentary processes that control the grain size and facies distribution of the SDF deposits at the channel-lobe transition zone, which are of interest in the petroleum industry as they can be potential reservoirsos flujos de sedimentos marinos por densidad (FSD) en la localidad de Mizala (Cuenca de Sorbas, SE de España) se depositaron durante el Tortoniense tardío en un sistema de abanico submarino medio, en las proximidades de la zona de transición canal-lóbulo. Los depósitos de canal y lóbulo están compuestos por 6 tipos de facies que corresponden a debritas, turbiditas de alta y baja densidad y a depósitos hemipelágicos autóctonos. Los resultados muestran la transformación de FSD a la salida de los canales como consecuencia de saltos hidráulicos. Se interpreta que una subida relativa del nivel del mar pudo condicionar el patrón de apilamiento del sistema de canal-lóbulo. Este estudio contribuye a entender los procesos sedimentarios que controlan la distribución de tamaños de grano y facies en depósitos de FSD de la zona transición canal-lóbulo, los cuales tienen un elevado interés en la industria de hidrocarburos ya que constituyen excelentes rocas almacé

Submarine landslide morphometrics and slope failure dynamics along a mixed carbonate-siliciclastic margin, north-eastern Australia

Comparatively little work has been carried out on the morphology and distribution of submarine landslides on mixed carbonate-siliciclastic margins. The morphometric analysis of 84 open slope submarine landslides on the Great Barrier Reef (GBR) margin of north-eastern Australia provides useful insights into slope failure dynamics and frequency distribution of landslides on mixed margins. Our analysis has revealed that the slope area affected by failures (12.6% of the margin) is similar to siliciclastic-dominated passive margins, although the total volume of remobilized sediment (73 km3) is comparatively small. Landslide scars lie at shallower depths to the south of the margin (mean of 576 m vs 1517 m to the north) and there is good correlation between the depth at origin and depth at termination for the GBR landslides. The cumulative frequency distribution of volume, area and total length of the GBR landslides does not fit to common distributions (e.g., power law, logarithmic or exponential) for the entire dataset. Still, the cumulative frequency distribution of landslide dimensions can be statistically explained either by a power law similar to other passive margins, or by a lognormal distribution similar to some siliciclastic margins. Morphometric characteristics, such as the volume of sediment released per unit width and the probability function of volume distribution suggest that slope failures mainly involved relatively unconsolidated sediments. We find that the disintegration by debris flows was the dominant process along the entire GBR margin and that their spreading efficiency and mobility was relatively low. Margin stratigraphy, fluid overpressure at the base of the slope, and detachment surfaces at the boundary between different lithologies that separate sedimentary cycles may have preconditioned the slope to fail. This compilation provides a robust morphometric framework that allows comparison with existing and future slope failure databases, and lays the foundation for performing numerical simulations to assess the landslide-generated tsunamigenic hazards along the GBR margin

Morphometric analysis of the submarine landslides in the central Great Barrier Reef margin, north-eastern Australia

The morphometric characterization of the submarine landslides on a mixed siliciclastic-carbonate margin, the Great Barrier Reef (NE Australia), is presented in this study. The landslides cover about the 27% of the slope in the study region, removing in some examples up to 33 km 3 of sediment. Spearman rank correlation coefficients show meaningful correlations among landslide size parameters. However, there is no relationship between the unfailed slope in the source area and the size of the landslide. The mobility of the landslides is within the normal range observed in other submarine landslides worldwide. The results of this study represent a preliminary step to understand the sedimentary processes, preconditioning factors and triggering mechanisms for submarine landslide generation in mixed marginse presentan los resultados de la caracterización morfométrica de los deslizamientos submarinos en un margen continental mixto siliciclástico-carbonatado, el margen de la Gran Barrera de Arrecifes (NE Australia). Los deslizamientos abarcan aproximadamente el 27% de la superficie del talud en la zona de estudio, removilizando en algunos casos volúmenes de sedimento de hasta 33 km3. El análisis de correlación de Spearman indica que existe buena correlación entre los parámetros relacionados con las dimensiones del deslizamiento. Sin embargo, no se observa relación directa entre la pendiente del talud y las dimensiones de los deslizamientos. La movilidad de los deslizamientos se encuentra dentro del rango observado en otros deslizamientos submarinos. Los resultados de este trabajo constituyen un primer paso para entender los procesos sedimentarios y mecanismos de generación de deslizamientos en los márgenes de tipo mixt

An enigmatic kilometer-scale concentration of small mytilids (Late Miocene, Guadalquivir Basin, S Spain).

Upper Miocene heterozoan carbonates crop out extensively in a NE-SW-trending belt (42 km long and 1.5-8 km wide) along the so-called El Alcor topographic high, from Carmona to Dos Hermanas (Seville, S Spain). These carbonates formed at the southern active margin of the Guadalquivir Basin, the foreland basin of the Betic Cordillera. They change to marls basinward (NE) and to sands landward (SE and SW). Therefore, carbonate production was constrained to a limited area in an otherwise siliciclastic shelf. The carbonates (up to 40 m thick) overlie a gradually coarsening-upward succession of marls followed by silts and sandstones. The carbonate sequence can be divided into three subunits corresponding, frombottom to top, to lowstand, transgressive, and highstand system tract deposits. The lower subunit, exhibiting extensive trough cross-bedding, is interpreted as a shallow-water bar deposit. The intermediate subunit onlaps underlying sediments and was deposited in deeper, lowturbulence conditions. The upper subunit deposits accumulated in a well-oxygenated outer platform based on benthic foraminiferal assemblages. The presence of hummocky and swaley cross-stratification in these latter deposits suggests that theywere affected by storms. Pervasive fluid-escape structures are also observed throughout the carbonates. The three subunits consist of bioclastic packstones to rudstonesmade up of abundant fragments of smallmytilids. Isotopic data from serpulid polychaete Ditrupa tubes show 13C-depleted values (up to −16.1¿), whereas δ18O yields normal marine values. Additional isotopic data on shells of scallops, oysters, and small mussels, as well as bulk sediment, show diagenetic alterations. Based on actualistic examples of massive concentrations of mussels, the nearly monospecific composition of the El Alcor deposits, together with negative δ13C values of Ditrupa tubes, indicates that cold seeps presumably promoted carbonate formation. However, the absence of typical features of cold-seep deposits, such as authigenic carbonatesmediated by anaerobic bacterial activity and the typical chemosynthetic shelly organisms, makes the large carbonate body of El Alcor an unusual cold-seep deposit

Late Quaternary multi-genetic processes and products on the northern Gulf of Cadiz upper continental slope (SW Iberian Peninsula)

On continental margins, the upper slope to shelf break environment forms a critical region where sediment supply, hydrographic activity and gravitational processes determine how and when sediments are partitioned between the shallow- and deep-marine realm. On the SW Iberian margin, relatively few studies have addressed the dynamics of this region, although it holds key information regarding the link between the sedimentary evolution of the continental shelf and the contourite depositional system on the middle slope. This work therefore presents a high-resolution analysis of the morphological and stratigraphic expressions of late Quaternary (dominantly last glacial and present-day interglacial) sedimentary processes on the upper slope and shelf margin sector between 7° and 7°30’ W. The integration of seismic, bathymetric and hydrographic data reveals the presence of alongslope processes and products (a bottom current-related plastered drift, moat, erosional surface and terrace, an internal wave-/tide-controlled sediment wave field), downslope (gravitational) processes and products (an upper slope – shelf margin valley system, slumps, debrites, gullies), neotectonic elements (diapirs) and fluid flow features (pockmarks, bright spots). The spatial distribution of these features indicates that the study area becomes increasingly alongslope-dominated towards the W, and oppositely, more downslope-dominated towards the E, because sediment supply to the latter area is enhanced under the dominant eastward dispersal of fluvially supplied sediments on the shelf. In addition, glacial-interglacial variations in the amount of sediments supplied to the shelf edge and the intensity of oceanographic processes in the study area also generate a distinct temporal variability, with glacial and interglacial intervals respectively recording principally downslope- and alongslope-controlled morphological elements. Finally, regardless of these overall spatial and temporal patterns, diapirism and fluid flow are inferred to locally destabilize sediments and induce small-scale mass wasting in the study area. These findings are not only relevant to the northern Gulf of Cadiz, but also to the general understanding of sedimentary dynamics and controls in mixed downslope- and alongslope-controlled upper slope to shelf margin settings worldwide.T. Mestdagh is funded through a doctoral scholarship of the Ghent University Special Research Fund (BOF). We would like to thank the captains, crews and scientists involved in research campaigns COMIC 2013 on board of RV Belgica and LASEA 2013 on board of RV Ramón Margalef. Ship time on RV Belgica was provided by BELSPO and RBINS-OD Nature. This research was performed in collaboration with ”The Drifters” Research Group of the Royal Holloway University of London (UK), and is associated to projects CTM 2012-39599-C03 , CGL2016-80445-R ‘SCORE’ ( AEI/FEDER , UE), CTM2016-75129-C3-1-R , CGL2011-30302-C02-02 and CTM2017-88237-P . Editor Michele Rebesco and two anonymous reviewers are kindly acknowledged for providing constructive feedback

Incised valleys on the Algarve inner shelf, northern Gulf of Cadiz margin: stratigraphic architecture and controlling factors in a low fluvial supply setting

A network of cross-shelf paleovalleys has been recognized over the paleo-inner shelf off the Gila & SIM;o-Almargem Estuary, a small fluvial drainage system that presently receives minor sediment supply in the eastern Algarve shelf, northern margin of the Gulf of Cadiz (SW Iberian Peninsula). This study is aimed at determining the driving controls that triggered substantially different paleohydrological conditions and sedimentary dynamics of ancient fluvial systems in this margin. We focus on evidences of secondary controls on valley genesis and evolution, superimposed to primary glacio-eustatic control such as antecedent geology, low fluvial supply and changing hydrodynamic regimes. The architecture and spatial distribution of these paleovalleys were interpreted based on a grid of seismic profiles with different resolutions. Likewise, a sediment core obtained in a distal position of the paleovalley system provided information about sedimentary processes during the most recent stage of valley infilling. The chronostratigraphic framework was constructed based on regional seismic horizons defined in previous studies and complemented with two AMS 14C dates obtained from bivalve shells.The inner shelf paleovalley system is composed of several incised valley features which exhibit a remarkable similar internal architecture. These inner valley features exhibit two major incision phases (from oldest to youngest; IP 2 and IP 1) that are thought to constitute a simple paleovalley system formed during the last glacial cycle. The origins of the incision are considered to be different. The older one is related to fluvial incision during the sea-level fall leading into the Last Glacial Maximum, whereas the recent one is interpreted as the result of tidal scour during the postglacial transgression. Their corresponding infillings are interpreted, respectively, as estuarine bay-fill deposits and estuary-mouth sands. Overlying the paleovalley infilling, a distinctive reflective unit is in agreement with the generation of coastal barriers and related depositional systems.The formation of the paleo-inner-shelf paleovalley system was strongly conditioned by antecedent geology, which strongly limited the generation of wide incised valleys and determined the amount of incision landward of a well-defined break of slope. Its postglacial infilling was mainly estuarine in nature, likely involving the development of a dendritic system, with numerous barriers interrupted by tidal inlets and channels in a mixed estuarine system with low fluvial supply.Research projects CGL2011-30302-C02-02 and PID2021-125489OB-I00, supported by Spanish Ministries of Economy and Competitiveness and Science and Innovation. LA/P/0069/2020info:eu-repo/semantics/publishedVersio

Origin and driving mechanisms of marine litter in the shelf-incised Motril, Carchuna, and Calahonda canyons (northern Alboran Sea)

Introduction and methodsMarine litter density, distribution and potential sources, and the impact on canyon seafloor habitats were investigated in the Motril, Carchuna and Calahonda canyons, located along the northern margin of the Alboran Sea. During the ALSSOMAR-S2S oceanographic survey carried out in 2019, canyon floor imagery was collected by a Remotely Operated Vehicle along 5 km in the Motril Canyon, 10 km in the Carchuna Canyon, and 3 km in Calahonda Canyon, together with 41 surficial sediment samples. Additionally, coastal uses, maritime traffic and fishing activity data were analyzed. A 50 m resolution multibeam bathymetry served as base map. ResultsIn the Motril and Calahonda canyons, the density of marine litter was low and the material was dispersed, very degraded and partially buried. In contrast, the Carchuna Canyon contained a greater amount and variety of litter. The Carchuna Canyon thalweg exhibited a density of marine litter up to 8.66 items center dot 100 m(-1), and litter hotspots with a density of up to 42 items center dot m(2) are found along the upper reaches of the canyon thalweg. DiscussionLow litter abundances found in the studied canyons most likely reflect low population densities and the absence of direct connections with streams in the nearby coasts. The high shelf incision of the Carchuna Canyon and its proximity to the coastline favor littoral sediment remobilization and capture as well as the formation of gravity flows that transport the marine litter along the thalweg toward the distal termination of the channel. Litter hotspots are favored by the canyon morphology and the occurrence of rocky outcrops. Most debris is of coastal origin and related to beach occupation and agricultural practices in the adjacent coastal plain. A third origin was represented by fishing gear in the study area. Fishing activity may be producing an impact through physical damage to the skeletons of the colonial scleractinians located in the walls of the Carchuna Canyon. In contrast, the Motril and Calahonda canyons can be considered passive systems that have mainly acted as depositional sinks in the recent past, as evidenced by buried marine litter.18-ESMARES2-CIRCA project of the Instituto Español de Oceanografıa; DL57/2016/CP1361/CT0009info:eu-repo/semantics/publishedVersio

Middle Eocene Nummulites and their offshore re-deposition: a case study from the Middle Eocene of the Venetian area, northeastern Italy

The Middle Eocene Calcari nummulitici formation from northeast Italy, Venetian area, represents a shallow-marine carbonate ramp developed on the northern Tethyan margin. In the Monti Berici area, its main components are larger foraminifera and coralline red algal communities that constitute thick carbonate sedimentary successions. Middle ramp and proximal outer ramp environments are recognized using component relationships, biofacies and sedimentary features. The middle-ramp is characterized by larger flattened-lenticular Nummulites on palaeohighs between which rhodoliths formed. Larger Nummulites palaeohighs containing N. millecaput, N. crassus, N. discorbinus and N. cf. gizehensis developed more basin-wards. The following relatively quiet environments basin-wards of the palaeohighs represent areas of maximum carbonate production. The transition between the distal middle- and the proximal outer-ramp settings is marked in the study area by a large erosional surface which is interpreted to have been formed as a result of an erosive channel body filled in by deposits re-sedimented from shallower depths. These off-shore re-sedimented channelized deposits, ascribed to the Shallow Benthic Zone SBZ 15, lying on hemipelagic marls (planktonic foraminiferal zone E9 (P11) allow for a biostratigraphic correlation to the Late Lutetian. The studied deposits, represented by packstone to rudstones, were displaced while still unlithified. The Lutetian-Bartonian regression along with the local tectonic activity promoted the production of a high amount of biogenic shallow-water carbonates mainly produced in the Mossano middle-ramp settings. These prograded toward the basinal areas with high-sedimentation rate of carbonate deposits characterized by the larger Nummulites rudstones. Such high amounts of sediment led to sediment instability which potentially could be mobilized either by return currents due to occasional major storms or earthquakes induced by tectonic activity. These will have led to the offshore re-deposition of the Nummulites sediments into deeper water setting via the observed channels. Since potential migration pathways are short, such distal re-sedimented channel-fill material surrounded by hemipelagic marls are optimally placed for the formation of potential subsurface oil reservoirs